Summary Thermosonication (TS) is an emerging nonthermal processing technique used for the liquid food preservation and is employed to improve the quality and acceptability of grapefruit juice. In this study, fresh grapefruit juice samples were subjected to TS treatment in an ultrasonic cleaner with different processing variables, including temperature (20, 30, 40, 50 and 60 °C), frequency (28 kHz), power (70%, 420 W) and processing time (30 and 60 min) for bioactive compounds, inactivation of enzymes pectin methylesterase (PME), peroxidase (POD) and polyphenolase (PPO) and micro‐organisms (total plate count, yeasts and moulds). The micro‐organism activity was completely inactivated in the treatment (60 °C for 60 min). The TS treatment at 60 °C for 60 min exposure reduced PME, PPO and POD activity by 91%, 90% and 89%, respectively. Results indicate that the advantages of TS for grapefruit juice processing at low temperature could enhance the inactivation of enzymes and micro‐organisms and it can be used as a potential technique to obtain better results as compared to alone.

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Summary The grapefruit juice was sonicated in an ultrasonic bath at 28 kHz frequency (amplitude 70%), for 0, 30, 60 and 90 min at 20 °C. This research was focused on the effects of ultrasound treatment on phenolic compounds, minerals, viscosity, lycopene, total anthocyanins, total carotenoids, micro‐organism analysis and sugars. A statistically significant increase was observed in total carotenoids, lycopene, sugar contents (sucrose, glucose and fructose) and phenolic compounds, whereas a decrease in viscosity and micro‐organisms were found in all the grapefruit juice samples sonicated for 30, 60 and 90 min as compared to control. However, maximum improvement was observed in the sonication treatment for 90 min. The results of this study suggest that ultrasound treatment may improve the quality of grapefruit juice.

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